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The MPCV will take humans beyond the ISS, to destinations such as Mars

Nasa has confirmed that the vehicle it will use to send astronauts to places like asteroids will be based on its Orion capsule concept.

Orion was the ship being built to return America to the Moon before the project was cancelled last year by President Barack Obama.

The US space agency says the financial investment and the engineering lessons learned should not be wasted.

It wants the new Multi-Purpose Crew Vehicle to benefit from that heritage.

Mr Obama has said he would like humans to visit a space rock in the 2020s. The MPCV would be the ship that takes them there. It would also have a role in any human mission to Mars - the destination Nasa is aiming to reach in perhaps the 2030s.

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Orion was conceived as a high-spec vehicle that could visit the ISS and do deep-space destinations

Lockheed Martin was the American company leading the development of Orion. It will keep the prime contractor role on the new ship.

"We are committed to human exploration beyond low-Earth orbit and look forward to developing the next generation of systems to take us there," said Nasa Administrator Charles Bolden in a statement.

The MPCV will be capable of carrying four astronauts on 21-day missions. It would start those journeys by launching on the top of an as-yet-undefined big rocket and end them by splashing down in the Pacific off California.

Nasa says the 23-ton spacecraft would have a pressurized volume of 19.5 cubic metres (690 cu ft), just over nine cubic metres (300 cu ft) of which would be habitable.

On missions longer than 21 days, the MPCV would be attached to other modules.

"During these missions to asteroids or Mars, or to the moons of Mars, this vehicle would be just maintained in more dormant mode while the crew would be in another volume which would have longer-term consumables and capability to support them," explained Doug Cooke, associate administrator for the agency's Exploration Systems Mission Directorate in Washington.

"In terms of deep space exploration, we hope to have test flights obviously in this decade. We're not exactly sure when, but certainly as early as possible. Those would be missions beyond low-Earth orbit."

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Investment in Orion has already topped $5bn

Orion was one of the centrepieces of former President George W Bush's Constellation programme, which sought to return Americans to the Moon using two new rockets and a high-spec capsule.

But the initiative was cancelled by his successor because of its burgeoning cost - $9bn at the time Mr Obama ordered it be shut down. Investment in Orion alone to date is put at slightly more than $5bn.

Many commentators expected elements of Constellation to re-surface in whatever programme replaced it, and some sort of Orion derivative was an obvious prospect.

But Nasa moved swiftly on Tuesday to correct the idea that the adoption of the MPCV was somehow a move on the part of the agency to protect "old ways" of doing business.

Mr Cooke said the Orion government and industry team had shown exceptional creativity in finding ways to push costs down.

However, he could not say what the final development bill would be or how much the recurring costs would be on operational MPCVs.

Nasa will also need at some stage to define a heavy-lift rocket to put in orbit the MPCV and any associated exploration equipment.

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The SpaceX company claims its Dragon capsule will also be a highly capable vehicle

The US Congress, through the Nasa Authorisation Act 2010, has mandated that this rocket should be launching by the end of 2016, although the agency has previously stated that it views this timeline as challenging. It promises more details on the launcher "in the coming weeks".

Nasa's current fleet of space vehicles - the shuttles - are being retired, with the Atlantis orbiter set to end their operation for good with a final flight in July.

America will then rely on Russian Soyuz vehicles to get its astronauts to the International Space Station (ISS) until a new wave of US commercial carriers enter service around the middle of the decade.

In the main, these crew carriers will be substantially cheaper to build and operate than the MPCV, and will not be capable of venturing beyond low-Earth orbit where the ISS resides.

However, the SpaceX company claims the Dragon capsule it is developing for journeys to the ISS will eventually be able to match any task given to the Lockheed Martin ship, and do it at a greatly reduced price.